Ongoing Research Project Descriptions

Title: Enhanced Clay Membrane Barriers for Sustainable Waste Containment
Investigators: Charles D. Shackelford, Michael A. Malusis (Bucknell University), and Jeffrey C. Evans (Bucknell University)
Sponsor: U. S. National Science Foundation
Project Period: 10/01/06 - 09/30/10
Description: This research project is a collaborative effort between Colorado State University, a Research I institution, and Bucknell University, a predominantly undergraduate institution (PUI). The overall goal of the proposed research is to evaluate the concept of simultaneously improving both the efficiency and duration of waste containment through the use of clay barriers that exhibit membrane behavior by enhancing the attenuation capacities of the clay barriers. Membrane behavior represents the ability of clays to restrict or prevent the movement of chemical species (contaminants), but not the water in which the chemical species are dissolved. This research goal is based on the results of recent studies documenting both (a) the existence of membrane behavior in clays used as barriers for waste containment applications (e.g., landfills), and (b) the beneficial reduction in the potential for contaminants to penetrate the barrier resulting from the existence of membrane behavior in clay barriers. However, research to date also has indicated that clay membrane behavior is susceptible to potential time-dependent degradation during migration of the contaminants through the barriers. This susceptibility to membrane degradation conceptually can be offset by enhancing the attenuation (sorption) capacity of the clay by adding materials with high sorption capacities (e.g., processed zeolites and activated carbon) to the clay. The resulting increase in sorption capacity hinders or retards contaminant migration such that the membrane behavior is sustained for a longer period of time. However, the potential effect of the additive material requires evaluation, for example, to ascertain the amounts of additive material required, the effectiveness of the additive material in sustaining the existence and efficiency of the membrane behavior, and the potential for any adverse interaction of the additive material on the observed membrane behavior of the clay.

Title: Bentonite-Polymer Nanocomposites for the Geoenvironment
Investigators: Charles D. Shackelford, Craig H. Benson (University of Wisconsin-Madison), and Gerald W. Darlington (CETCO)
Sponsor: U. S. National Science Foundation
Project Period: 08/01/08 - 07/31/11
Description: This research project focuses on modifying bentonite at the nanoscale to improve its stability for sustainable performance in a variety of geoenvironmental applications. Modification will involve inserting large organic molecules between crystalline montmorillonite layers comprising the bentonite at the nanoscale, and then polymerizing these molecules after insertion. This process will yield a more rigid structure that retains the large organic molecules thereby providing permanence. The modified material, known as a bentonite-polymer nanocomposite (BPN), is expected to retain the useful advantages of conventional bentonites, while being more resistant to long-term instability due to factors commonly encountered in geoenvironmental applications. Aside from resulting in superior barriers, seals, and sorbents that can provide considerable reduction in the risk to human health and the environment, BPNs also could revolutionize the way bentonite is used worldwide and impact a wide range of industries. The research involves characterizing the physical, chemical, mineralogical and hydraulic properties of the BPN and comparing these measured properties with those associated with the base bentonite used to produce the BPN and/or other natural bentonites. The research project also represents an interdisciplinary, collaborative effort among researchers at three universities and an industrial partner (CETCO, or Colloidal Environmental Technologies Corporation), and will stimulate cross-fertilization among industry researchers, faculty, and students. Efforts include involving undergraduate students in the research as well as women and minorities.

Title: Critical Assessment of Coupled Flow Behavior in Unsaturated Clay Barriers
Investigators: Charles D. Shackelford and Ning Lu (Colorado School of Mines)
Sponsor: U. S. National Science Foundation
Project Period: 09/15/09 - 08/31/12
Description: The goal of this research, which is a collaborative effort between Colorado State University and the Colorado School of Mines, is to evaluate the existence and significance of chemico-osmosis and membrane behavior in unsaturated clays. A collaborative experimental and theoretical approach will be employed to achieve this goal. The overall objectives are: (1) to develop and evaluate an innovative apparatus for measuring membrane behavior and quantifying coupled fluid and chemical transport in unsaturated clays; (2) to clarify the direct and coupled driving forces governing fluid and chemical fluxes; (3) to measure governing parameters on unsaturated soils under conditions representing practical problems; (4) to develop a model for solute transport under unsaturated conditions that incorporates membrane behavior; and (5) to quantify the importance of coupling as a function of the degree of saturation and solute concentration in soils typical of barrier materials. This research has both intrinsic scientific merit in terms of the fundamental theory being developed and the parameters being measured as well as practical implications in terms of improving our ability to predict the rate at which solutes migrate through clays under unsaturated conditions. This research also is transformative from the perspective of representing a fundamental challenge to the appropriateness of the widely used Darcy-Buckingham law for fluid flow and Fick's law for chemical transport in unsaturated clays.

Title: Experimental and Computational Investigations for Consolidation-Induced Contaminant Transport for High Water Content Geo-Materials
Investigators: Charles D. Shackelford and Patrick J. Fox (University of California-San Diego)
Sponsor: U. S. National Science Foundation
Project Period: 07/01/10 - 06/30/13
Project Description: The goal of this project, which is a collaborative research effort between Colorado State University and the University of California at San Diego, is to advance the state-of-the art with respect to our understanding of the mechanisms and significance of consolidation-induced contaminant transport for high water content geo-materials. The phenomenon of coupled consolidation and contaminant transport occurs for a variety of practical applications in geotechnical and geoenvironmental engineering. Such applications include confined disposal of contaminated high water content geo-materials (e.g., tailings, dredgings, sludges, and slurries) in ex situ engineered impoundments, mechanical dewatering of contaminated high water content geo-materials, in situ remediation of source zones contaminated with chlorinated solvents via injection of granular zero valent iron (ZVI) slurry and soil mixing, and in situ capping of subaqueous contaminated sediments. The proposed research will consist of a fundamental experimental and computational investigation of the mechanism of consolidation-induced contaminant transport for several materials and conditions, and then assess the significance of these findings for relevant geotechnical and geoenvironmental applications. The research plan has six tasks: (1) material procurement and characterization; (2) material property testing; (3) consolidation-induced transport testing; (4) development and validation of computational models; (5) computational simulations; and (6) project collaboration and dissemination of results. The proposed research has both intrinsic scientific merit in terms of a fundamental assessment of this transport mechanism and associated parameters as well as practical implications in terms of improving our ability to predict contaminant outflows from high water content geo-materials during consolidation. As a result, a better understanding of the mechanism and significance of consolidation-induced contaminant transport will be achieved, thereby enhancing the ability of designers and regulators to protect the public health and the environment from the effects of contaminants. Results from this research have the potential to transform the way contaminated high water content geo-materials are currently characterized, handled, dewatered and/or disposed.